W/o seeing the chart yet, might be night time antenna orientation away from you. KTCT has a smaller night time footprint, KFAX doesn't have a coverage map, but is 50,000 watts 24 hours. It may hit you w/lower signal strength though at night time. 
Edit: Looking at your original bitloading chart I clearly see a spike at 860 kHz for KTRB, it has a night time change too.
Chris
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